Various techniques have in the past been employed to coat the interiors of hollow articles and, more particularly, the shell or body of two-piece metal cans. Typically, such coatings are applied from a spray nozzle, which is positioned adjacent the open end of the can shell for delivery of the coating material thereinto. However, the spray patterns of conventional spray nozzles are such that the resultant coatings tend to be nonuniform, thus requiring the over-spraying of certain areas of the can so as to provide a necessary minimum coating on other areas. The problem is particularly acute in the case of can bodies made by drawing and ironing either tinplated or tin-free steel and intended for use with carbonated beverages, since they require especially heavy, uniform, void-free coatings to prevent corrosion and product contamination.
While attempts have been made to improve upon the aforementioned spray pattern deficiencies (see, for example, the spray nozzle described in U.S. Pat. No. 3,737,108), so far as is known no presently available nozzle provides a spray pattern which is capable of uniformly covering, in a single operation, the interior surfaces of a can body having one open and one closed end. Consequently, it has been found necessary to apply the spray coating in two applications, with the initial coating being cured prior to the second spray application; without such curing, the combined weights of the two coatings, as heretofore applied, would cause them to run and sag, and to accumulate in the corners of the can.
While entirely satisfactory from the standpoint of producing good quality coatings within the can shell, such a "double coat" technique is rather inefficient, in requiring either two passes of the can shell through the spraying and curing apparatus, or a single pass through two spraying and curing stations. Thus, the technique is disadvantageous in that it entails high capital expenditures for equipment, excessive plant space, energy, manpower and materials; moreover, the can shells are subjected to possible abuse as a result of the amount of handling which the double-coat process may involve.
Accordingly, it is an object of this invention to provide a novel method for producing a relatively heavy, uniform and continuous coating on the interior surfaces of hollow articles.
It is also an object of the invention to provide such a method wherein the efficiency of the coating operation is maximized.
Another object of the invention is to provide such a method wherein capital expenditures, and requirements of space, energy, manpower and materials are minimized, without sacrifice to the quality of the coating produced.
A more specific object of the invention is to provide a novel method having the foregoing features and advantages, which method is particularly beneficial for the coating of can shells fabricated by drawing and ironing steel blanks.